Merge changes Icfd32d0a,Icc9ff4d4,Ieee07502,I559eeb1f,Iaf2a6f6d, ...

* changes:
  Use java language 1.9 for sdk_version: "current"
  Remove special case for sdk_version: "none"
  Use system modules for turbine
  Make javaVersion an enum
  Move TestConfig sdk versions forward
  Split java 8 and 9 classpaths in TestClasspath

java/aar.go

@@ -538,6 +538,10 @@ func (a *AARImport) targetSdkVersion() string {
 	return a.sdkVersion()
 }
 
+func (a *AARImport) javaVersion() string {
+	return ""
+}
+
 var _ AndroidLibraryDependency = (*AARImport)(nil)
 
 func (a *AARImport) ExportPackage() android.Path {